#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;
const int N = 510, M = 10010;
int n, m, k;
struct Edge
{
    int a, b, c;
} edges[M];
int dist[N];
int last[N];

void bellman_ford()
{
    memset(dist, 0x3f, sizeof(dist));
    dist[1] = 0;
    for (int i = 0; i < k; ++i)
    {
        memcpy(last, dist, sizeof(dist));
        for (int j = 0; j < m; ++j)
        {
            auto e = edges[j];
            dist[e.b] = min(dist[e.b], last[e.a] + e.c);
        }
    }
}
int main()
{
    scanf("%d %d %d", &n, &m, &k);
    for (int i = 0; i < m; ++i)
    {
        int a, b, c;
        scanf("%d %d %d", &a, &b, &c);
        edges[i] = {a, b, c};
    }

    bellman_ford();
    if (dist[n] > 0x3f3f3f3f / 2)
    {
        puts("impossible");
    }
    else
    {
        printf("%d", dist[n]);
    }
    return 0;
}